Harvest Aid Products and Timing in Soybean

by Jeremy Ross and Tom Barber - August 18, 2025

With the 2025 soybean harvest season starting in Arkansas, we’re starting to get calls about what is the proper timing for harvest aid applications and what products work the best.  With the weedy fields I’ve seen driving across the state due to either preemerge herbicides not being activated early in the season, or the poor control from or lack of post-herbicide applications, we could potentially see more harvest aids applied this fall to help with harvesting our soybean crop.  A lot of work has been conducted on the use of harvest aids in the mid-South U.S. and below are results from research conducted here in Arkansas.

Timing of Harvest Aids

The most frequently asked question about the use of harvest aids in soybean is at what growth stage (GS) can these products be applied and reduce significant yield and seed quality issues.  In 2022 and 2023, I walked 1000’s of acres where harvest aids were applied too early, and significant yield reduction and poor seed quality was seen due to missed timed applications.  From research conducted by Dr. Tom Barber using Gramoxone SL applied at 0.25 lb ai/ac at five different growth stages, the earliest growth stage where we see no statistical yield loss is R6.5 GS.  However, the data from this research still indicate a 6.6% grain yield reduction with the R6.5 GS application compared to the UTC.  If applications of these products are made prior to R6.5 GS, soybean grain yields were reduced by as much as 68.5% when applied at R5.5 GS and 56.6% when applied at R6.0 GS compared to the untreated check (Table 1).  The results from this research are similar to results seen in other mid-South U.S. states.  The hardest part of this recommendation is determining when the soybean plants are at R6.5 GS.  Under normal growing conditions, soybean plants will reach the R6.5 GS 10-14 days after R6.0 GS.  The definition of R6.0 GS is “One pod containing a green seed that fills the pod cavity at one of the four uppermost nodes on the main stem with a fully developed leaf.”  At the R6.0 GS, when soybean pods are opened, the pod membrane will still stay attached to the seed (Figure 1).  When soybean plants reach the R6.5 GS, seed from a pod from one of the four uppermost nodes should easily separate from the pod membrane.  At this point, the seed is not taking in any additional moisture or nutrients.  A visual progress of pod development from R6 to R8 is shown in Figure 2.  Based on the current data, the University of Arkansas System Division of Agriculture’s recommendation for timing of harvest aid on soybean is R7.0 GS.  The R7.0 GS is when one mature-colored pod is anywhere on the main stem.  This GS is visually easier to identify than the R6.5 GS and no grain yield loss was seen compared to the UTC.

Adapted from “A Visual Guide to Soybean Growth Stages”, University of Wisconsin – Madison.

Harvest Aid Products

Nine different harvest aid products or tank mixes of these products were evaluated for soybean desiccation at the R6.5 GS and at 70% leaf drop. When compared to the soybean grain yield of the untreated check, yields for all of the products and combinations at the two timings were not significantly different.  All treatments with Gramoxone SL alone or in combination and Sodium Chlorate alone had significantly higher percent leaf drop seven days after application compared to the other treatments at the R6.5 GS timing.  All treatments had greater than 95% leaf drop at both timings 14 days after applications (data not shown).  For weed desiccation, if heavy weed pressure is present a combination of paraguat (Gramoxone) 10.67oz/A, and Sharpen 1oz/A plus 1% MSO is recommended. Coverage is critical for vine and weed desiccation, so higher water volumes are recommended.  The only downside to the use of paraquat is the pre-harvest interval of 15 days. Always read and follow herbicide labels.

Things to remember about the use of harvest aids:

• Do not apply when wind is blowing towards immature neighboring crops
• Apply harvest aids to soybean at the R7.0 GS or later to minimize yield loss. Applications applied earlier than R7.0 GS could decrease grain yield and increase the likelihood of poor seed quality resulting in dockage discounts.
• Harvest aids such as Gramoxone SL do not remove excessive moisture from seeds. There are some reports that adding sodium chlorate to a desiccant may help remove excessive moisture from green soybean tissue and/or seed.
• If possible, do not apply a harvest aid herbicide prior to rainfall. Wetting and drying cycles could cause shattering of pods to occur.
• Be prepared to harvest fields as soon as possible as allowed on the herbicide label, after applying a desiccant. Once harvest aids are applied to a soybean field, nothing good can happen to the crop until it is put through the combine.
• Crop and weed desiccation may be slowed during cool, wet weather. Additional time beyond the herbicide product’s pre-harvest time interval may be needed to dry down large weeds.
• Preharvest intervals are 15 days following Gramoxone (paraquat), 7 days following glyphosate, 3 days following Aim or Sharpen and 0 days following sodium chlorate.